Because of the increasing electrification of the devices for providing vehicle functions, a performance increase of the central electrical supply unit in motor vehicles is necessary. The electrical supply unit has heretofore only been provided by a so-called starter battery, e.g., a lead accumulator, when the motor vehicle is out of service, e.g., the internal combustion engine is shut down. Another name for a lead accumulator is lead-acid battery. In addition, a generator is available to provide a source voltage when the internal combustion engine is running or started.
To achieve a performance increase of the supply unit, a promising approach is to provide a multiple battery supply in the vehicle electrical system of the motor vehicle. For this purpose, a high-performance store which has small dimensions in relation or in comparison, and which is generally based on the lithium-ion battery, and an electrical store having larger dimensions in relation thereto in the form of the known lead accumulator can be provided. The direct connection of the two batteries is produced via the vehicle electrical system as a parallel circuit.
Said increased performance capacity is achieved in this way, but a different system behavior of the electrical supply unit also results. If an electrical load is put into operation and therefore consumes an electrical current from the vehicle electrical system, it is thus dependent on the interaction of the batteries connected in parallel with the vehicle electrical system which voltage results in reaction to the supply current required by the load. However, if possible one would wish to predict this or know it beforehand, so that if necessary the start of the load can be blocked, if the voltage dip induced by the supply current would interfere with the operation of other electrical loads. In other words, an estimation of the voltage dip upon loading of the vehicle electrical system, in particular by a high power load, for example, an electrical starter or a compressor motor, is of interest.
A method for avoiding voltage dips when switching on electrical loads in a motor vehicle is known from DE 102 32 539 A1. After a switching-on request, the peak power available in the vehicle electrical system is ascertained and the switching-on time for the load is chronologically delayed such that the peak power required by the load is also guaranteed to exist at the switching-on time.
A motor vehicle having a generator and two electrical batteries is known from DE 10 2011 054 582 A1, wherein power paths for conducting electrical currents are established by a switching unit of the motor vehicle.